Spread of bacteria during hypothermia

In seeking an explanation for the deaths of mammals soon after their apparently complete rehabilitation from extreme degrees of experimental hypothermia, factors other than direct damage at a tissue or cellular level, or interference with normal physiological mechanisms, should not be overlooked. One outcome of lowering an animal’s body temperature well below 0° C might be a reduction of the efficiency of the endothelial lining of the gut as a barrier against the ingress of potentially harmful organisms, such as saprophytes, into the tissues of its body. This might come about through small scattered foci of tissues damaged by cold injury (chilling of the mucus membranes of the nasopharyngeal region may, so it has been suggested, help one to ‘catch’ a cold) possibly in con­junction with a temporary falling into abeyance of phagocytic activity. It would certainly be unwise in this context to assume that bacterial activity is depressed by reduction in temperature to an extent comparable with the activity of mammalian tissue cells. Spread of infection might even commence before restoration of the blood circulation for, as those who have been concerned with the problems of obtaining tissues for surgical replacement are aware, micro-organisms do spread through a cadaver fairly rapidly after death. If such a leakage or spread of organisms—especially saprophytic types—did occur through hypothermia, their subsequent proliferative activity might well be enhanced by the products of any cell destructions occasioned by cold injury. The probable stressed condition of an animal after experimental hypothermia might also depress the activity of its immunological defence mechanism.

Effects of cellular constituents of mycobacteria on the resistance of mice to heterologous infections I. Protective effects

Vaccination with living attenuated tubercle bacilli (BCG) was found to increase the resistance of mice to infection with virulent staphylococci. An even more striking protective effect could be elicited by intraperitoneal or subcutaneous injection of small amounts (0.1 mg. or more) of killed BCG cells. The killed BCG cells retained most of their protective activity after prolonged heating at acid, neutral, or basic reactions-and after extraction with acetone, methanol, and NaOH (at pH 10.5). Some protective activity could be recovered in a fraction soluble in methanol at 55 degrees C. The protective effect against infection manifested itself in a prolongation of survival time following infection, and also in the fact that smaller numbers of staphylococci were recovered from the organs of infected mice. Both types of effects were still evident 10 weeks after vaccination. Injection by the intraperitoneal route of killed cells of BCG, or of methanol extracts of them, elicited in mice a high level of protection against intravenous injection of Myco. fortuitum. A protective effect quantitatively and qualitatively similar to that elicited by BCG, resulted from the intraperitoneal or subcutaneous injection of killed cells of Myco. fortuitum.

Effects of cellular constituents of mycobacteria on the resistance of mice to heterologous infections. II. Enhancement of infection

Injection of certain cellular constituents of mycobacteria into mice simultaneously with, or shortly after, infection with Staph. aureus or with Myco. fortuitum, markedly shortened the life of the infected animals. This infection-enhancing effect could be achieved by injecting the cellular constituents by either the intravenous, the intraperitoneal, or the subcutaneous route. Suspensions of killed mycobacteria were injected into mice which had been infected several months before with small doses of various bacterial pathogens and which still harbored small numbers of living organisms in their organs. Under these conditions, a marked increase in the numbers of living bacteria in the organs of the treated mice could be detected within a very few days after treatment with the mycobacterial products, and a certain percentage of the animals died rapidly. One of the first and most constant manifestations of the change in the infectious process from the chronic to the acute state was the appearance of a large microbial population in the liver. This happened even though Staph. aureus and Myco. fortuitum are rapidly cleared from the liver of normal mice. In addition to killed cells of BCG and of Myco. fortuitum, pertussis vaccine and the purified lipopolysaccharide (endotoxin) of Gram-negative bacilli also proved capable of converting chronic bacterial infections into acute infectious processes.